a) Field of the Invention
This invention relates to a driving device capable of being preferably utilized for moving a stage for optical examining apparatus, such as microscopes, having a pair of moving beds capable of traveling in directions normal to each other, straight guide members, one member being mounted on one side of each of the moving beds, driving knobs extending in a direction normal to planes along which the moving beds travel, coaxially arranged to render the moving beds travel, and a transmission mechanism arranged between the driving knobs and the straight guide members, converting a rotary motion of each of the driving knobs into a rectilinear motion through each of the straight guide members of the moving beds.
b) Description of the Prior Art
From the fact that the stage driving device of this type is suitable for use in microscopes for examining large-sized wafers in a semiconductor fabrication process, those of many types have been proposed in the past. Each such device is designed so that when the stage is coarsely moved, its movement is easy, while when finely moved by means of the driving knob, it is braked and is not moved without cause even though external force is applied to the stage.
These conventional devices are broadly classified according to their structural features into two ways: a brake system constructed, for instance, as proposed by Japanese Utility Model Publication No. Sho 56-19050 and Japanese Patent Preliminary Publication No. Sho 61-246714, so that rotary wheels concentrically integral with driving knobs whose amounts of turning effects are rendered very small are always engaged with straight guide members of moving beds and the movement of a stage in an ordinary state is smoothly conducted. While in the operation for fine adjustment, frictional members cause pressed force to be applied to the stage or a driving knob shaft for braking, and a clutch system constructed, for example, as proposed by Japanese Patent Preliminary Publication Nos. Sho 57-45513, Sho 57-99607 and Sho 61-198206, and Japanese Utility Model Preliminary Publication No. Hei 1-153509, so that the entire driving knob shaft can directly be disengaged from the straight guide members of the moving beds by cams or the like (which is hereinafter referred to as a direct type) and so that an intermediate transmission wheel is disposed between a driving shaft meshing always with the straight guide members of the moving beds and the driving knob shaft and is pressed against the driving shaft and the driving knob shaft at once in the operation for fine adjustment (which is hereinafter referred to as an indirect type).
Of the above conventional stage driving devices, the brake system has the problem that continuous engagement of rotary wheels integral with the driving knob shaft with the straight guide members of the moving beds, renders it inevitable to bring about the deterioration of performance attributable to wear. The difficulty about the assembly requires accuracy such that the straight guide members must be arranged parallel to the traveling directions of the moving bed. The increase of production costs caused by the use of expensive bearings for smooth rotation of the driving knob shaft is also a problem. In the direct type clutch system, when the elements of the driving knob shaft are engaged with the straight guide members, the concentricity of these elements renders it difficult to position the elements of the driving knob shaft corresponding to individual straight guide members and, as a result, the driving knob shaft is often strongly pressed only against one of the straight guide members. Therefore, the difficulties are encountered that one of the straight guide members is considerably worn and the difference of the amount of driving force arises between the moving beds arranged in a pair. Further, the indirect type clutch system has a problem similar to the brake system because the straight guide members engage always with the driving shaft. This system has another problem similar to the direct type clutch system in view of the operation such that the intermediate transmission wheel is pressed against the driving shaft and the driving knob shaft at once. Also, in order to solve the problems caused by the direct type clutch system, the proposal has been made in the past that resilient member wheels, for example, made of rubber, are secured to the driving knob shaft so as to be engaged with and disengaged from the straight guide members. This method, however, raises a problem that when the moving beds are once fed in positioning the stage and the driving knobs are released, the moving beds are moved by the resilience of the resilient member wheels and the stage is shifted from a desired position. Additionally, there is another problem that the use of such wheels in the semiconductor fabrication process will form the source of dust in a clean room. Also, in order to solve the problems caused by the resilient member wheels made of rubber or the like and caused when the elements of the driving knob shaft are pressed against the straight guide members at once, the device constructed to make no use of the resilient member wheels has been proposed by the above Sho 61-198206. However, it has the problem that the structure is extremely complicated with the resultant high cost.